1. FIELD OF THE INVENTION
The present invention relates to an electronic material used as an insulating material for an oxide superconductor such as YBa.sub.2 Cu.sub.3 O.sub.6+.delta., (Tl,Pb)Sr.sub.2 CaCu.sub.2 O.sub.7, or the like.
2. DESCRIPTION OF RELATED ART
Compounds such as (Eu,Ce).sub.2 (Eu,Ba).sub.2 Cu.sub.3 O.sub.8+z, wherein 0z.ltoreq.2, and (Pb,Cu)(Sr,Eu).sub.2 (Eu,Ce).sub.2 Cu.sub.2 O.sub.9, which both have the structural unit similar to that of YBa.sub.2 Cu.sub.3 O.sub.6+.delta. which is a 90K class superconductor, (Tl.sub.0.5 Pb.sub.0.5)Sr.sub.2 CaCu.sub.2 O.sub.7, and TlBa.sub.2 CaCu.sub.2 O.sub.7 which are a 80K class superconductor are known.
These compounds are disclosed in, for example, Yoshiki Tokura, "Solid State Physics", Vol. 25, 1990, pp. 618-636.
However, since these compounds have a structure comprising a YBa.sub.2 Cu.sub.3 O.sub.6+.delta. -type structural unit or TlBa.sub.2 CaCu.sub.2 O.sub.7 -type structural unit and a single fluorite-type structural unit [(R,Ce)O.sub.2 ]alternately put on each other, they have an electric resistance lowered when the oxide superconductor such as YBa.sub.2 Cu.sub.3 O.sub.6+.delta., (Tl.sub.0.5 Pb.sub.0.5)Sr.sub.2 CaCu.sub.2 O.sub.7 or the like is made together with them while heat treating. Therefore, these compounds do not adequately function as the insulator for the superconductor.